Wedge Gate Valve Introduction

How does a wedge gate valve work?

A wedge gate valve is a type of multi-turn valve that uses a rising or non-rising stem. The stem rotates several times to either start or stop the valve. The valve begins by rotating the handwheel in a clockwise direction. Turning the handwheel makes the stem rotate as it moves upwards. The upward movement of the stem also makes the valve disc move upwards. As such, the valve is made open, allowing fluid to flow through the valve. Fluid flow keeps going on unless the valve is closed. The valve is closed by rotating the handwheel in the anticlockwise direction. As such, the stem rotates as it moves downwards. The downward linear movement of the stem forces the valve disc to return to its seating position. As such, the valve’s central hole where the fluid flows through gets blocked, which stops the valve. The valve then gets closed, and no fluid flows.

Figure: Working of a wedge gate valve.

Applications of wedge gate valve 

• Wedge gate valves are used in a crude oil refinery.
• They are used in the transportation of oil and gas.
• These valves are used in chemical processing industries.
• Wedge gate valves are used in steam power plants to control the flow of water used in cooling and heating.
• They are used in manufacturing paper and pulp as they hardly get clogged.
• These valves are used in mining applications to control the flow of slurries and sludge.

Advantages of wedge gate valves 

• These valves are suitable for both high-pressure and high-temperature applications.
• Wedge gate valves allow bi-direction fluid flow without causing mechanical damage to the valve.
• These valves have a low-pressure loss, which helps save energy and enhance efficiency.
• These valves are highly reliable in stopping and allowing fluid flow.
• These valves are available in various sizes, allowing different flow rates and pressure.
• Wedge gate valves are versatile as they are fit for use in various industrial applications.
• These valves are durable, mainly when used as shutoff valves.

Disadvantages of wedge gate valves 

• These valves are unsuitable for throttling fluid flow.
• Wedge gate valves are slow to open and close, unlike other valves like ball valves.
• These valves have their seats and disc prone to wear.
• They are prone to noise and vibration when not fully open.

Troubleshooting wedge gate valves 

The valve needs high operating torque to open/close. 

• Gland flange misalignment. Re-align the gland flange. Also, check if the stem is damaged, and if it is, replace it.
• The gland bolt is highly stressed. Loosen the gland bolt to reduce packing friction. However, do not make it too loose to avoid fluid leakage.
• Solids clogged between gland flange and stem. Open the gland bolt and clean of foreign objects.

The valve does not close/open completely. 

• There are foreign materials stuck in the valve. Disassemble the valve according to the wedge gate valve manufacturer’s instructions and remove foreign objects.
• Damaged seats. Replace the valve seats.
• Damaged stem. Replace the stem.

Leakage through the stem packing 

• Misalignment of the gland flange. Re-align the gland flange properly.
• Loose gland bolt. Tighten the gland bolt.
• Worn out packing. Replace the gland packing.

Leakage through the gasket 

• Misalignment on the bonnet. Re-align the bonnet and body properly.
• Loose bolts/screws. Tighten the connecting bolts or screws.
• Worn out gasket. Replace the gasket.

Leakage through the valve body/bonnet 

• Excess fluid pressure. Ensure the fluid pressure is at the range recommended by the wedge gate valve manufacturer.
• Loose connection. Tighten the screws/bolts connecting the body to the pipe or the body to the bonnet as necessary.
• Worn out seats. Replace the valve seats.

Summary 

Wedge gate valves are valves that operate by using a wedge disc to start or stop fluid flow. The valve uses a wedge-shaped gate (disc) to enhance the high seating area to ensure the valve can seal perfectly to the body. This type of valve operates using a manual handwheel or actuators like electric or pneumatic. Whether the valve is operated manually or using actuators, the working principle is to turn the valve stem so that the valve disc can move upwards or downwards. When the stem rotates to move up, it forces the disc to open the valve for fluid flow. On the other hand, when the stem turns to move downwards, it causes the disc to move downwards, where it finally closes any fluid flow. The choice of temperature level depends on the valve seat material. Seats made from metallic materials are ideal for temperatures above 65o C, while rubber or plastic are used below 65oC. Wedge gate valves are suitable for use in high and low temperatures.

Wedge gate valve manufacturers produce varieties of these valves, among them rising stem valves, non-rising stem valves, electrically actuated valves, and pneumatically actuated valves. Applications of these valves include chemical industries, water supply, power plants, mining, foods and beverages, paper, and pulp, among others. The advantages of this type of valve are that it is easy to clean and repair, versatile in size, has bi-directional fluid flow, low-pressure loss, and high strength.